Showing papers on "Claisen rearrangement published in 1973"
TL;DR: In this article, a charge-induced [3 s, 3 s] sigmatropic rearrangement of allyl aryl ethers with an alkyl group in the o-position, in the presence of boron trichloride, was studied.
Abstract: Allyl aryl ethers which have no strongly electron attracting substituents undergo a charge-induced [3 s, 3 s] sigmatropic rearrangement in the prescence of 0.7 mole boron trichloride in chlorobenzene at low temperature, to give after hydrolysis the corresponding o-allyl phenols (Tables 1 and 2). The charge induction causes an increase in the reaction rate relative to the thermal Claisen rearrangement of ∼1010. With the exception of allyl 3-methoxyphenyl ether (5), m-substituted allyl aryl ethers show similar behaviour (with respect to the composition of the product mixture) to that observed in the thermal rearrangement (Table 3). The rearrangement of allyl aryl ethers with an alkyl group in the o-position, in the prescence of boron trichloride, yields a mixture of o- and p-allyl phenols, where more p-product is present than in the corresponding product mixture from the thermal rearrangement (Table 4). This ‘para-effect’ is especially noticeable for o-alkylated α-methylallyl aryl ethers (Table 5 ).
With boron trichloride, 2,6-dialkylated allyl aryl ethers give reaction products which arise, in each case, from a sequence of an ortho-Claisen rearrangement followed by a [1,2]-, [3,3]- or [3,4]-shift of the allyl moiety (Tables 6 and 7). Ally1 mesityl ether (80), with boron trichloride, gives pure 3-ally1 mesitol (95). From phenol, penta-ally1 phenol (101) can be obtained by a total of five O-allylations followed by three thermal and two boron trichloride-induced rearrangements.
The sigmatropic rearrangements of the ethers studied, using D- and 14C-labelled compounds, are collected in scheme 2; only the reaction steps indicated by heavy arrows are of importance.
With protic acids, there is a [3,3]-shift of the allyl group in 6-allyl-2,6-disubstituted cyclohexa-2,4-dien-l-ones, while with boron trichloride the [3,3]-reaction is also observed along with the much less important [1,2]- and [3,4]-transformations (Table 8). 4-Allyl-4-alkyl-cyclohexa-2,5-dien-1-ones give only [3,3]-rearrangements with boron trichloride (Table 9). As expected, the naphthalenone 112, which is formed by allowing boron trichloridc to react for a short time with allyl (1-methyl-2-naphthyl) ether (111), undergoes only a [3,4] rearrangement (Scheme 3).
Representations of how, in our opinion, the complex behaviour of allyl aryl ethers and allyl cyclohexadienones under the influence of boron trichloride, can be rationalized are collected together in Schemes 4 and 5.
In the last part of the discussion section, the steric factors leading to the appearance of the ‘para-effect’, are dealt with (Scheme 6).
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TL;DR: In this article, a successful Claisen rearrangement of a number of 1,4-diaryloxy-2-butynes is reported, which offers a facile synthetic route to tetracyclic derivatives resembling the naturally occurring pterocarpans.
29 citations
TL;DR: In this paper, it is suggested that initially a [3s, 3s]-sigmatropic rearrangement of the aryl propargyl ethers to the 6-allenyl-6-halogeno-cyclohexa-2, 4-dien-1-ones occurs and that from these the isolated products are formed via radical pathways.
Abstract: 7-Chloro-2-chloromethyl-benzofuran (13) and 3, 8-dichloro-2 H-1-benzopyran (12) are the main products from the thermal rearrangement (230–260°) of 2, 6-dichlorophenyl propargyl ether (7). Compounds 17, 18 and 19 are also formed, but in much smaller amounts (scheme 2 and table 1). However, in the case of the bromo-compounds 8 and 9 the rearrangement products are the benzofuran derivatives 21 and 22, containing one bromine atom less per molecule (scheme 4).
The corresponding naphthyl propargyl ethers 10 and 11 can be rearranged much more easily (180°) to the halogeno-naphthofurans 24 and 26 respectively. In the case of the bromo-ether 11, 2-methyl-naphtho[2, 1-b]furan (25) is also formed (scheme 5).
If the propargylic hydrogen atoms in 7 and 11 are replaced by deuterium atoms, then after rearrangement the deuterium atoms in the products d-13 and d-26 are found in the β-positions to the oxygen atom of the furan ring (schemes 3 and 5).
It is suggested that initially a [3s, 3s]-sigmatropic rearrangement of the aryl propargyl ethers to the 6-allenyl-6-halogeno-cyclohexa-2, 4-dien-1-ones (e.g.a) occurs and that from these the isolated products are formed via radical pathways (scheme 6).
Under neutral conditions aryl propargyl ethers containing a free ortho-position give on heating benzopyran derivatives [2]. When this thermal reaction is carried out in sulfolane in the presence of powdered potassium carbonate, 2-methyl-benzofuran derivatives are formed (table 2). This leads to the possibility of preparing, depending on the conditions, either benzopyran or benzofuran derivatives by the Claisen rearrangement of aryl propargyl ethers. The mechanism for the formation of the benzofurans is given in scheme 9.
27 citations
TL;DR: The potential of a Claisen followed by a Cope rearrangement is illustrated by the reactions of 3-methylhept-6-en-1-yn-3-ol (II) and 5-isopropylidene octa-trans-3,7-dien-2-one (III).
Abstract: The synthetic potential of a Claisen followed by a Cope rearrangement is illustrated by the reactions of 3-methylhept-6-en-1-yn-3-ol (II). This propargylic alcohol (II) condenses with methyl isopropenyl ether with Claisen rearrangement to give 6-methyldeca-4,5,9-trien-2-one (IV), which isomerises in boiling xylene through the product of Cope rearrangement (V) to 5-isopropylideneocta-trans-3,7-dien-2-one (VI). The acetate (IX) of the alcohol (II) undergoes an analogous series of rearrangements to the allenyl acetate (X) and the dienyl acetate (XII).
17 citations
Abstract: 2,3-Dideoxy-4-O-vinylhex-2-enopyranoside derivatives on heating to 180° undergo the Claisen rearrangement to give 2,3,4-trideoxy-2-C-(formylmethyl)hex-3-enopyranoside isomers. Suprafacial [3,3] sigmatropic processes are involved, so that stereochemical integrity is maintained at the allylic centres. The reaction represents a novel means whereby branch points can be introduced into carbohydrates.
16 citations
TL;DR: In this paper, a synthesis of (±)-bakuchiol methyl ether, involving Claisen rearrangement of geranyl vinyl ether as the key step, is described, and further thermal reorganisation of the intermediate 3-vinyl-citronellal is discussed.
13 citations
12 citations
TL;DR: In this paper, the substitution reactions of 4-hydroxybenzo [b]thiophen and its 3-methyl derivative are described and modified Gattermann conditions and bromination with N-bromosuccinimide gave the 5substituted product in each case, whereas treatment with bromine in carbon tetrachloride gave a corresponding 5,7-dibromo-compound.
Abstract: Electrophilic substitution reactions of 4-hydroxybenzo [b]thiophen and its 3-methyl derivative are described. Formylation under modified Gattermann conditions and bromination with N-bromosuccinimide gave the 5-substituted product in each case, whereas treatment with bromine in carbon tetrachloride gave the corresponding 5,7-dibromo-compound. Nitration in acetic acid gave a mixture of the 5-nitro-, the 7-nitro-, and the 5,7-dinitro-compounds, of which the 5-nitro-compound was the major component in each case. Claisen rearrangement of 4-allyloxybenzo[b]thiophen and its 3-methyl derivative gave the appropriate 5-allyl-4-hydroxy-compound. Fries rearrangement of 4-acetoxybenzo[b]thiophen with aluminium chloride in boiling benzene gave a mixture of 7-acetyl-4-hydroxybenzo[b]thiophen (90%) and its 2,3-dihydro-derivative (7%). Similar treatment of 4-acetoxy-3-methylbenzo[b]thiophen gave a mixture of 7-acetyl-4-hydroxy-3-methylbenzo[b]thiophen (21%) and the 2-acetyl isomer (68%). Bromination of 4-methylsulphonyloxybenzo[b]thiophen in acetic acid gave a mixture of 3-bromo-(60%) and 5-bromo-4-methylsulphonyloxybenzo[b] thiophen (20%) and the corresponding 5,7-dibromo-compound (6%), together with two unidentified products. 3-Bromomethyl-4-methylsulphonyloxybenzo[b]thiophen, obtained by treatment of the corresponding 3-methyl compound with N-bromosuccinimide. was used as a key intermediate in the synthesis of 2-(4-hydroxy-3-benzo[b]thienyl)ethylamine, the sulphur analogue of 4-hydroxytryptamine.
TL;DR: In this article, the structure of angelicone is reassigned as 17 and the synthesis of glabralactone (17) has been achieved from the methyl ether of 7 via retro-Michael chromanone ring opening, and coumarin ring isomerisation.
TL;DR: A number of possible synthetic routes to 8,9dihydro-8,8,9-trimethylphenaleno[1,2-b]furan-7-one and its 1,6-dimethoxy-(21a) and 1-hydroxy-6-methoxy(21c) analogues have been explored as discussed by the authors.
Abstract: A number of possible synthetic routes to 8,9-dihydro-8,8,9-trimethylphenaleno[1,2-b]furan-7-one (21 b) and its 1,6-dimethoxy-(21a) and 1-hydroxy-6-methoxy-(21c) analogues have been explored. One successful method involved acid-catalysed cyclisation of the keto-lactone (22)[2-(2,7-dimethoxy-1-naphthoyl)-3,3-dimethylpentan-4-olide]; another utilised the Claisen rearrangement of the dimethylallyl ether (24b)[9-hydroxy-4-methoxy-3-(3-methylbut-2-enyloxy)phenalenone].
TL;DR: The Claisen rearrangement of the steroid dienone 6, on heating at 120°, was rearranged by [3s, 3s]-sigmatropic processes to form 52% of 2-(1′-methylallyl)- and 48% of 4′-(1-dihydroxy-estra-1,3,5,(10)-triene (7 and 8, respectively).
Abstract: Pure 10β-(trans-2′-butenyl)-17β-hydroxy-estra-1,4-dien-3-one (6), 10-(trans-2′-butenyl)-2-oxo-Δ1(9),3(4)-hexahydronaphthalene (13), trans-2′-butenyl 17β-hydroxy-3-estra-1,3,5-(10)-trienyl ether (12) and trans-2′-butenyl 5,6,7,8-tetrahydro-2-naphthyl ether (14) were prepared by direct C- and O-alkylation, respectively, of the corresponding phenols (cf. [3] [10]), namely estra-3, 17β-diol and 5,6,7,8-tetrahydro-2-naphthol.
The Claisen rearrangement of the ether 14 (200°, 12 h) yielded 53% 1-(1′-methylallyl)- and 34% 3-(1′-methylallyl)-5,6,7,8-tetrahydro-2-naphthol (15 and 16, respectively), whereas in the thermal (120°, 14 h) and in the acid-catalysed (boron trifluoride in ether, 20°, 20 min) reaction of the corresponding dienone 13 nearly equal amounts of 15 (53–54%) and 16 (46%) were formed by thermal and charge-induced aromatic [3s, 3s]-sigmatropic rearrangements [2].
The steroid dienone 6, on heating at 120°, was rearranged by [3s, 3s]-sigmatropic processes to form 52% of 2-(1′-methylallyl)- and 48% of 4′-(1′-methylallyl)-3, 17β-dihydroxy-estra-1,3,5,(10)-triene (7 and 8, respectively). The steroid phenols 7 and 8 were carefully separated; subsequent hydrogenation (Raney-Ni in alcohol) and ozonolysis yielded 2-methylbutyric acid (9): from 7, S-(+)-9, and from 8, R-(−)-9, obtained in 88,5 and 88,0% optical purity (cf. [4a]). This means (cf. scheme 2 and Table 2) that both phenols are formed to the extent of at least 94% via a chair-like activated complex, and of at most 6% via a both-like activated complex (ΔΔG = 2.15 kcal/mol). Similarly, the boron trifluoride-induced rearrangement of 6 (born trifluoride in ether, 0°, 45 min) yielded 7 and 8, from which S-(+)-9 and R-(−)-9 were respectively obtained in 89% and 98% optical purity. For these induced rearrangements this corresponds to at least 94,5 and 99%, respectively, of the chair-like, and to only 5.5 and 1% of the boat-like activated complex (ΔΔG = 1.5–2.5 kcal/mol). These results demonstrate that the activated complexes of both [3s,3s]-sigmatropic processes, i.e. the pure thermal reaction at 120° and the charge-induced reaction occurring at 0°, must be very similar. Thus, the boron trifluoride accelerates the Cope-like reactions 6 7 + 8, but does not influence the geometries of their transition states.
The Claisen rearrangement of the steroid ether 12 (200°, 15 h), yielding 7 and 8, was not influenced by the chiral steroid skeleton, because no optical induction was observed (both phenols, 7 and 8, yielded on degradation racemic 2-methylbutyric acid (9)).
TL;DR: In this article, the same sequence of reactions was carried through with two methyl derivatives of the hexadienol (Ia), and two successive Cope rearrangements into the linear 2,6-dimethyltetradeca-2,6,9,13-tetraenal (XV), also formed in the same way from the rearranged isomer (XI) through Claisen rearrangement.
Abstract: Condensation of hexa-1,5-dien-3-ol (Ia) with 1,1,3-triethoxy-2-methylbutane, catalysed by o-nitrobenzoic acid, proceeds with elimination of three moles of ethanol to form an intermediate dienol ether that undergoes Claisen rearrangement to 2-methyl-2-vinylocta-4,7-dienal (Va). At higher temperatures (ca. 160°) this aldehyde (Va) rearranges to 2-methyl-5-vinylocta-2,7-dienal (VIa), which at still higher temperatures (ca. 190°) equilibrates through a second Cope rearrangement with the more stable 2-methyldeca-2,5,9-trienal (VIIa). The same sequence of reactions was carried through with two methyl derivatives of the hexadienol (Ia).Reduction of the aldehyde (VIa) formed the allyl alcohol (X), which rearranged to the same dimethylated straight-chain alcohol (XI) as was produced by reduction of the isomer (VIIa). Condensation with 1,1,3-triethoxy-2-methylbutane converted (X) through Claisen rearrangement and two successive Cope rearrangements into the ‘linear’ 2,6-dimethyltetradeca-2,6,9,13-tetraenal (XV), also formed in the same way from the rearranged isomer (XI) through Claisen rearrangement and one Cope rearrangement.
TL;DR: In this paper, the formation of the allyl aryl ether is rationalised as involving a [1,5] acetyl shift. But this is not the case in the case of allyl ether.
Abstract: Thermal rearrangement of the allyl aryl ether (5) gave, in addition to the expected Claisen rearrangement product (6), the isomer (7), and similarly thermal transformation of the allyl ether (8) gave the mixture (9) and (10); the formation of (7) and (10) is rationalised as involving a [1,5] acetyl shift.
TL;DR: Six new imidazolinone glyoxylates, which exist in tautomeric equilibria with hydroxyimidazole glyoxyles, were synthesized by a new type of Claisen rearrangement and evaluated in a neuropharmacological mouse profile.
TL;DR: In this article, 3,3-Dialkylallyl alcohols and aldehyde dimethyl acetals condense with Claisen rearrangement to form substituted pent-4-enals.
Abstract: 3,3-Dialkylallyl alcohols and aldehyde dimethyl acetals condense with Claisen rearrangement to form substituted pent-4-enals. The hexa-1,5-dienes made from these aldehydes by the Wittig reaction then rearrange in the opposite direction according to Cope. While this scheme worked very well with n-heptanal dimethyl acetal and 3-methylbut-2-en-1-ol, yielding 2-methyldodeca-2,6-diene, it was less successful when applied to an attempted synthesis of ‘propylure’[(5E)-10-propyltrideca-5,9-dienyl acetate].
TL;DR: In this paper, a Claisen-type sigmatropic rearrangement of 3-carboxyprop-2-ynyl vinyl ethers was used to synthesize 4-hydroxy-3,3-dimethyl2-vinylidenebutan-4-olide (V), and corresponding aldehyde ester [ethyl 2-(1-formyl-1-methylethyl)buta-2,3dienoate (VIII)].
Abstract: Naturally occurring 4-hydroxy-2-vinylbut-2-en-4-olide (V), an allenic analogue [4-hydroxy-3,3-dimethyl-2-vinylidenebutan-4-olide (VII)], and the corresponding aldehyde ester [ethyl 2-(1-formyl-1-methylethyl)buta-2,3-dienoate (VIII)] have been synthesised by a Claisen-type sigmatropic rearrangement of 3-carboxyprop-2-ynyl vinyl ethers.
TL;DR: In this article, the 3-methylbut-2-enyl ethers of tropolone and 3,5,7-trimethyltropolone proceed in refluxing n-nonane with migration of the ether residue to both 3 and 5 positions.
Abstract: Thermal isomerisations of 3-methylbut-2-enyl ethers of tropolone and 3,5,7-trimethyltropolone proceed in refluxing n-nonane with migration of the ether residue to both 3- and 5-positions. Where enolisation of the resulting cyclo-heptadienediones cannot occur the 5,5-disubstituted cyclohepta-3,6-diene-1,2-dione predominates in the resulting equilibrium.
TL;DR: In this article, triphenylphosphine was used in the thermal rearrangement of N-allyl-N-tosylaniline to 2-methyltosylindoline.
Abstract: The use of a small amount of triphenylphosphine in the thermal rearrangement of N-allyl-N-tosylaniline to 2-allyl-N-tosylaniline in N,N-dibutylaniline depressed, to a great extent, the decomposition of the reaction mixture. The sum of the yields of rearrangement products, which were 2-allyl- and 2-(trans-1-propenyl)-N-tosylaniline, and 2-methyl-1-tosylindoline, reached to 85%.
TL;DR: In this paper, the rates of rearrangement of 4-allyl-N-tosylamino (naphthal-n-methylimide) at 205, 215 and 225°C in 9 solvents have been determined.
Abstract: The rates of rearrangement of 4- (N-allyl-N-tosylamino) naphthal-N-methylimide (1) at 205, 215 and 225°C in 9 solvents have been determined. The rearrangement was a first order reaction in every case and so insensitive to the nature of the solvent that the rates varied within only a 3.4-fold range. Hydroxylic solvents such as ethylene glycol and phenol were relatively useful for accellerating the reaction. The entropies of activation had negative values.These results show that the rearrangement proceeds via a transition state similar to that of the usual Claisen rearrangement.
TL;DR: In this article, the kinetics of the Claisen rearrangements of allyloxynaphthoquinones (1) −(3) are reported for a range of solvents, and activation parameters are calculated for the rearrangement in different types.
Abstract: The kinetics of the Claisen rearrangements of the allyloxynaphthoquinones (1)–(3) are reported for a range of solvents, and activation parameters are calculated for rearrangements in solvents of different types. The Claisen rearrangement in protic solvents is shown to differ in mechanism from that in aprotic solvents. The relative ease of the rearrangements of (1)–(3) is discussed in relation to earlier predictions, and a transition-state model suggested on the basis of the observed solvent and structure effects. These studies are of relevance to the problem of the Claisen rearrangement in biological systems, and suggest that caution should be exercised in the design and interpretation of biosynthetic experiments in this area.